Stirrup, mounted shock combat, feudalism, and chivalry -- The classic theory of the origins of feudalism and its critics -- The origin and diffusion of the stirrup -- Mounted shock combat and the temper of feudal life -- The agricultural revolution of the early Middle Ages -- The plough and the manorial system -- The discovery of horse-power -- The three-field rotation and improved nutrition -- The northward shift of Europe's focus -- The medieval exploration of mechanical power and devices -- The sources of power -- The development of machine design -- The concept of a power technology